The process of staking is a known technique for securing articles in assembled relation and has found widespread application with plastic molded articles. Broadly, in this process a formable projection on one article is brought into registration with an aperture in another article to form the assembly. The projection may have been or can concurrently be prepared for staking, e.g. heat softened, and staked into a head shape by action of a forming die tool.
The retention strength of the staked joint is directly related to the integrity of the formed head. If the head is formed irregularly or only partially the area of retention will be reduced and the holding strength lessened. An irregularly or partially formed head can be caused by escape of fluent material from the site of the staking operation. Additionally, if the dimensions of the formable projections vary, a standard stroke or tool shape will cause spattering of material with an oversized projection, or underformation of the head with an undersized projection.
It is the objective of the present invention to provide a method and apparatus for staking formable projections that promotes uniform head formation and location to enhance retention strength.
The following United States patents are of interest as background art to the present invention: U.S. Pat. Nos. 2,705,346; 3,358,550; 3,591,996; 3,929,943; 4,377,549; and 4,456,576.